We plan to determine the role of the putative secreted virulence factor BopB in the pathogenicity of Burkholderia pseudomallei. BopB contains a motif that is related to those of the signature catalytic motifs of protein tyrosine phosphatases and inositol polyphosphate 4-phosphatases (CX5RT) vs (CX5RI). This suggests that it encodes a novel and heretofore undescribed class of phosphatase that has 2 human homologues and versions in numerous other species. Thus we plan to determine the effect of mutation of the critical C residue in BopB on assays of bacterial growth in infected macrophage cell lines as well as assays of escape from endocytic vesicles and the ability of the organism to cause cells to fuse. We will express and isolate recombinant BopB and its human homologues and determine their enzymatic activities in hydrolyzing inositol phosphates and/or protein tyrosine phosphates. These studies may allow us to define new reactions in inositol signaling and explain how perturbation of such reactions lead to the intracellular pathogenicity of B. pseudomallei. We hope to discover new potential antigens that might be used for vaccine development.